The following invention relates to an automatic dual side grinding machine for resharpening circular saw blades.
The above-mentioned patents, especially U.S. Pat. No. 4,823,649, provides an adjustable dual side grinding machine for circular saws that includes among its features the ability to grind successive teeth of the circular saw with a pair of reciprocating spindles supporting rotary grinding wheels on both the forward and reverse strokes. The purpose of the forward and reverse grinding strokes is to shorten the time necessary to regrind the teeth of the saw. If grinding is accomplished on the forward stroke only, and if the operator must wait for another forward stroke before advancing the next tooth to be ground, the operation will take twice as long as one in which successive teeth are ground on forward and reverse strokes. Another way of approaching this problem is to grind the teeth only on the forward stroke but to provide a quick retract mechanism to shorten the time between forward strokes. An example of this type of quick retract feature is shown in the U.S. Pat. No. 4,750,387 to Swiger. In the Swiger device the grinding wheels are advanced through the forward grinding stroke at a first rate of speed. A sensor detects the completion of this stroke and speeds up the motor to provide a fast retraction stroke thus speeding up the grinding cycle as a whole. The Swiger system, however, depends on the use of an electric motor having variable rates of speed. It is also necessary with the Swiger system to provide sensors to sense the completion of the forward grinding stroke and the rearward quick retract stroke and to signal the motor to change speeds.
The dual side grinder of U.S. Pat. No. 4,823,649 also provides some adjustments, namely, a tangential angle adjustment and a radial angle adjustment. The tangential angle adjustment is provided through a torsion bar which bears against an index finger mounted on a pivot. The torsion bar has a tendency at some settings to become unstable and to give variable readings to a displacement indicator which is calibrated to provide the precise angular adjustment for the index finger.
The, radial angle adjustment of U.S. Pat. No. 4,823,649 is accomplished by separately rotating a pair of cams disposed within slots provided in each of the spindle-supporting base plates to separately alter the radial angle of attack of each of the grinding wheels. This requires separate adjustments for each of the grinding wheels, and gives rise to the possibility that the radial angle for each side of the grinding operation will be unequal. Also, slight differences in the performance or calibration of the gauges on either side of the saw blade could result in differing radial angle adjustments.
In the past the spindles have been driven reciprocally by means of motors having output drive belts and it has been necessary to deal with the problem of placement of the motors. One solution to this problem, as discussed in the application of U.S. Pat. No. 4,846,023, is to suspend the motors below the spindles on plates and allow them to be carried reciprocally along with the spindles as they move relative to the frame. This adds considerable inertia to the spindle assemblies and therefore interferes with the ability of the spindle drive motors to provide an efficient and accurate grinding stroke and/or quick retract stroke.